1. Field of the Invention
The present invention relates to pesticidal compositions comprising a UV sensitive pesticide and a UV sunscreen, wherein the UV sunscreen protects the pesticide against inactivation by UV radiation. The present invention also relates to a method for protecting a UV sensitive pesticide against inactivation by UV radiation. The present invention further relates to methods for using the pesticidal compositions to control a pest.
2. Description of the Related Art
The efficacy of a pesticide against a target pest depends on the persistence of the pesticide in the environment. A number of factors, particularly environmental factors, are detrimental to a pesticide. One of the most important environmental factors is ultraviolet (UV) radiation. UV radiation may inactivate a pesticide if it possesses an absorption maximum in the range 300-380 nm.
For example, biopesticides including Bacillus thuringiensis crystal delta-endotoxins and spores, entomopathogenic viruses, entomopathogenic fungi, and nematodes are particularly subject to inactivation by UV radiation. Furthermore, some chemical pesticides including insecticides, fungicides, herbicides, rodenticides, molluscicides, miticides, ovicides, algicides, larvicides, bactericides, and nematocides are also sensitive to UV radiation depending on the chemical structure of the particular chemical pesticide.
The art has strived to protect pesticides against UV radiation in order to economically provide a pesticidal formulation with extended environmental persistence and thus improved efficacy as a pesticide. Efforts have been directed to protecting pesticides by combining the pesticide with a UV sunscreen that protects the pesticide against inactivation by UV radiation and preserves the pesticidal activity.
An example of UV sunscreens is lignin (Pogwaite and Shapiro, in Samsonm Vlak, and Peters (eds.), Proceedings, Fundamental and Applied Aspects of Invertebrate Pathology, Foundation of the Fourth International Colloquium of Invertebrate Pathology, Wageningen, The Netherlands, 1986). Martignoni and Iwai disclose that sodium lignosulphonate is useful as a UV protectant for Orgyia pseudotsugata NPV (1985, Journal of Economic Entomology 78:982-987). Allan discloses a method for controlling the release of pesticides using a lignin polymer by chemical covalent bonding of a pesticide to a lignin polymeric substrate (U.S. Pat. No. 3,813,236). Dimitri and Falkehag also disclose the physical bonding of a lignin polymer and a pesticide to form a controlled release system (U.S. Pat. No. 3,929,453). DelliColli et al. disclose the use of cross-linked lignin gels as pesticidal carriers in controlled release pesticide systems (U.S. Pat. Nos. 4,184,866 and 4,244,728). Moss and Lim also disclose a process for encapsulating a pesticidal agent in lignin (WO 92/19102). Lebo and Detroit further disclose a method to provide resistance of agriculturally active substances to UV degradation by microencapsulating the active substances in a lignosulphonate covalently linked to a protein (EP 0 653 158 A1).
Lignin is a principal constituent of the woody structure of higher plants. Lignin products include, for example, lignosulphonates, alkali lignins, and oxylignins which may be obtained from sulphite, sulphate, and alkali waste liquors (Snook, 1982, Handbook for Pulp & Paper Technologists, TAPPI, Atlanta). The properties of lignin products vary significantly with regard to temperature limit for stability (e.g., less than 95.degree. C. to less than 230.degree. C.); salt tolerance (e.g., less than 0.1% precipitate in a salt solution containing sodium chloride, magnesium chloride, and calcium chloride with concentrations of less than 70 ppm to less than 270 ppm total dissolved solids); surface tension (e.g., 45 to 65 dynes/cm for a 1% aqueous solution); molecular size (e.g., less than 20,000 to less than 100,000 based on a standard lignosulphonate having an average molecular weight of 34,000); sulphonic sulphur (e.g., less than 2.0% to less than 9.5% sulphonic sulphur expressed as % S on solids); pH (e.g., a pH from about 3.5 to about 11.0); reducing groups (e.g., 0 to about 22); and cation (e.g., Na, Ca, Mg, NH.sub.3, or Fe). The properties of some lignin products are described in the Borregaard Lignotech Bulletin entitled Specialty Chemicals for Pesticide Formulations.
While lignins have reportedly provided good results regarding the protection of pesticides against UV radiation, the results have not as yet made it possible to resolve critical problems necessary for obtaining commercially useful compositions which can be used in the field. Moreover, the art has not been able to identify the properties of a lignin material which provide commercially suitable protection of a pesticide against inactivation by UV radiation under field conditions.
It is an object of the present invention to provide pesticidal compositions with improved protection against UV radiation.